you discover that you cannot find Solutions under Web Designer Galleries or you may have noWeb Designer Galleries under your Site Collection Site Settings at all.

Default Sharepoint Online Site Collection Site Settings located here:

You may have something like

Some smart guys may also find Solutions Gallery and even button Upload Solution under URL:https://.sharepoint.com/_catalogs/solutions/Forms/AllItems.aspx

You may even try to Upload Solution Web Solution Package file (.wsp) there but you get permission error (I’ve already sent request)

Resolution.

Microsoft Sharepoint Online team rolled out a feature to limit the amount of scripting allowed in order to maintain the security and integrity of the sites in tenants. SharePoint Online tenants received the feature. When the scripting is disabled, the theme gallery, certain web parts, and other features that support scripting are no longer available to site collection owners or site owners. For more information, go to Turn scripting capabilities on and off.

The symptom that no Web Designer Galleries options is probably caused by this update. Please follow the steps below to validate this.

Sign in to Office 365 with your work or school account.

Go to the SharePoint admin center.

Select Settings.

Under Custom Script, check if custom script is disabled.

If you cannot see the Custom Script option or the settings are already Allow, please let Microsoft Support know. It may reflect a different issue.

If the settings are Prevent, you may switch the option to Allow so as to bring the custom scripting feature back. However, Microsoft doesn’t recommend you do this as custom scripts and solutions may cause unexpected security risk and load to your sites.

If you prefer to turn scripting on, please be acknowledged of this consequences:

If you want to enable scripting on Personal Sites, select Allow users to run custom script on personal sites

If you want to enable scripting on other user-created sites, such as Team Sites or Project Sites, select Allow users to run custom script on self-service created sites.

Select OK. It takes about 24 hours for the change to take effect.

Here is table you may find very interesting for your just purchased and out of the box secured Sharepoint Online tenant:

Features affected when scripting is disabled

When you disable scripting on personal sites or self-service-creation sites, the theme gallery, certain web parts, and other features that support scripting are no longer available to site collection owners or site owners. Any sites that used these features before scripting was disabled are still able to use them.The following site settings are no longer be available after scripting has been disabled:

Site feature

Behavior

Notes

Save Site as Template

No longer available in Site Settings.

You can still build sites from templates created before scripting was disabled.

Save document library as template

No longer available in Library Settings.

You can still build document libraries from templates created before scripting was disabled.

Solution Gallery

No longer available in Site Settings.

You can still use solutions created before scripting was disabled.

Theme Gallery

No longer available in Site Settings.

You can still use themes created before scripting was disabled.

Help Settings

No longer available in Site Settings.

You can still access help file collections available before scripting was disabled.

HTML Field Security

No longer available in Library Settings.

You can still use HTML field security that you set up before scripting was disabled.

Sandbox solutions

Solution Gallery will not appear in the Site Settings so you can’t add, manage, or upgrade sandbox solutions.

You can still run sandbox solutions that were deployed before scripting was disabled.

SharePoint Designer

Site Pages: No longer able to update web pages that are not HTML.

Handling List: Create Form and Custom Actionwill no longer work.

Subsites: New Subsite and Delete Site redirect to the Site Settings page in the browser.

Data Sources: Properties button is no longer available.

You can still open data sources.

Uploading an ASPX file to a document library

No longer available in document libraries.

ASPX files that are in the library already are not impacted.

The following web parts and features are unavailable to site collection owners and site owners after scripting has been disabled.